1. Field of the Invention
The present invention relates to a technology for optically scanning a surface of a commodity to read identification information attached to the surface of the commodity.
2. Description of the Related Art
In recent years, in distribution markets including supermarkets and department stores, it has been a widely-used practice to read barcodes attached to commodities using barcode readers for the checkout process and the management of the commodities.
With these barcode readers, the reading of barcodes are performed by irradiating a light beam such as a laser beam toward each barcode so as to scan the barcode surface and detecting the laser beam reflected by the barcode.
Generally speaking, a barcode reader uses a laser light source such as a semiconductor laser as the light source and scans a laser beam emitted from the laser light source by having the laser beam reflected by a rotating polygon mirror. The polygon mirror is a rotating member that has a set of flat-surface reflection faces on its periphery. It is possible to generate the scan beam by irradiating the light beam such as the laser beam onto the rotating polygon mirror. In the barcode reader, the scan beam generated this way is divided, using mirrors that are tilted at a plurality of mutually different angles, and emitted to the outside of the barcode reader through a reading window so as to be irradiated onto a barcode attached to a commodity, or the like.
The light beam reflected by the barcode becomes incident to the barcode reader through the reading window and then becomes incident to the polygon mirror by following the same path as the emission path. Because the reflection beams have been reflected diffusely, the barcode reader collects the reflection beams using a concave mirror, a transmission lens, or the like, so as to introduce the reflection beams to an optical detector. For example, see the Japanese Unexamined Patent Application Publication No. H11-109272.
FIGS. 5A and 5B are drawings for explaining conventional barcode readers. In the example shown in FIG. 5A, a laser light source 1 is disposed at an upper section of a barcode reader. In this arrangement, a laser beam emitted from the laser light source 1 goes through a through hole in a concave mirror 4 and becomes incident to the polygon mirror 2 so as to be scanned and emitted to the outside of the barcode reader. The light beam is then reflected by a barcode attached to a commodity, and follows the same path as the one used when being emitted outward before being reflected by the polygon mirror. After being collected by the concave mirror 4, the light beam becomes incident to an optical detector 3.
In the example shown in FIG. 5B, a laser light source is disposed at a lower section of a barcode reader. In this arrangement, the laser beam emitted from the laser light source 1 is deflected when being reflected by the laser beam deflecting mirror 5, and becomes incident to the polygon mirror 2. The laser beam is then scanned by the polygon mirror 2 and emitted to the outside of the barcode reader. Subsequently, the light beams reflected by a barcode attached to a commodity or the like are collected by the transmission lens 6 so as to become incident to the optical detector 3.
As described here, various arrangements and configurations are available for optical systems in barcode readers. To determine which ones of these arrangements and configurations are to be used, it is necessary to consider how to enhance the level of the reading performances of the barcode reader.
However, as in the barcode reader shown in FIG. 5A, when the laser beam emitted from the laser light source is directly incident to the polygon mirror, because the concave mirror is positioned between the laser light source and the polygon mirror, the dimension of the laser beam being incident to the polygon mirror is large in the path direction. As a result, the apparatus becomes large.
Normally, when being used in a supermarket or the like, because barcode readers are positioned between sales clerks and consumers, there is a demand for barcode readers that are small in size so that the sales clerks and the consumers are able to communicate with one another smoothly. In addition, it is more convenient to use barcode readers in a smaller size in order to prevent commodities and shopping baskets from getting in the way when they are moved around near barcode readers.
On the contrary, as in the barcode reader shown in FIG. 5B, when the laser beam emitted from the laser light source is incident to the polygon mirror after being deflected by the laser beam deflecting mirror, it is possible to dispose the laser light source and the polygon mirror on the same side with respect to the transmission lens. It is therefore possible to reduce the dimension of the laser beam being incident to the polygon mirror in the path direction, and to make the apparatus smaller. With this configuration, however, because the laser beam deflecting mirror is positioned between the transmission lens and the polygon mirror, part of the light beam being incident to the transmission lens is interrupted by the laser beam deflecting mirror. Thus, there is a problem that the amount of signal light reaching the optical detector becomes small, and the level of the reading performance of the barcode reader is lowered.